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Why is water in the fuel tank bad?
I mean, on the one hand it seems kind of obvious, if you had a fuel tank that was mostly water then you would lack combustible materials for the engine, but I get the impression that having any water in the fuel tank at all is considered a really bad idea.
Why is that?  Is it all right to have a very small amount of water in the fuel tanks?  Is there a defined percentage of liquid in the fuel tank that must be fuel in order to operate safely? (say 99.87% or something?)  And does this differ from prop to turboprop to turbofan to jet?

There will always be trace amounts of water suspended in the fuel; trace amounts don't cause problems.

Fuel systems are in general fed by gravity, at least until the fuel leaves the tank, where sometimes (always if the tank is lower than the engine) a pump pushes it toward the engine. This means that fuel is generally extracted from the bottom of the tank (or slightly above the very bottom to avoid having small particles from the bottom of the tank clogging up the fuel filter, incidentally this also introduces the concept of unusable fuel, as the stuff remaining at the bottom of the tank, although there are a lot more factors to this).
Fuel is less dense than water, meaning it'll float on top of the water. Or if you want to think of it the other way around, water is heavier and will sink to the bottom, right where you're trying to get your fuel to feed to the engine. Water doesn't burn very well and the engine will stop. Avgas is generally 0.72 kg/l and Jetfuel around 0.82 kg/l (water being 1 kg/l, see have SI units work well that way?).
A tiny amount of water probably mix with the fuel and simply reduce the power output slightly, whereas anything more will be drained from the tank first, and it'll be very hard to restart the engine. You'd have to pump all the water through the cylinder and out the exhaust, and I don't think this is generally possible in flight, especially right after takeoff which is generally the case when you have water in the fuel (could be right after switching tanks too though).
I don't know much about turbine engines, but I suspect they're less susceptible as the water will not prevent relighting the engine (the pumps will simply push the water out, there's no cylinder that could fill up with water), and you'll generally be using up more fuel on the ground making the problem readily apparent. This is pure speculation though.

For turbine engines, it's not as much the engines as it is the fuel system. With the lower temperatures they tend to fly in, the water can freeze into ice and clog up the fuel lines. British Airways 38 lost power and crashed on approach because of this. It can also cause issues with the fuel level sensors.

While water will separate from gasoline (avgas) to the bottom, it mixes and remains dispersed in jet fuel unless there is really a lot of it.

How about algae or fungus growing in the fuel tank? Would that be more of a problem with a lot of water?

@PhilPerry "stuff" living in the fuel is actually a real-world problem for jet fuel (and other kerosene/diesel fuels) - and does tend to get worse as the water content in the fuel rises (the "stuff" lives in the water and feeds at the water/fuel boundaries). It's enough of an issue that there are products specifically designed to deal with it..

@Steve Jessop, I think "because of ice" is a good answer to "why is water in the fuel bad". Although more water can mean more ice, it doesn't really answer the "tolerable quantity" part, but then neither does falstro's answer.

For anyone who's interested; a recent flame-out in Calgary was attributed to water in the fuel

Further long term problem if the tank contents are not drained is possible corrosion in the fuel tank (and also resulting debris from the corrosion contaminating the fuel).

@falstro Great answer... please don't forget... SI?

@CGCampbell I've linked SI to the corresponding wiki page. It's the international system of units, the abbreviation is from French.

Water in the fuel system is something of an over-inflated issue in aviation. Most aircraft have unusable sections of the fuel tank that will hold upwards of one gallon. That means that unless you have a gallon of water in the tanks it's unlikely that you'll be picking any up. We sump the tanks before every flight because it's easy to prevent an issue, and we're also pulling out any debris which is a much bigger issue than water. But if you're just running along and a bit of water sloshes into the fuel intake, it's unlikely that you'll even notice. Now obviously an engine can't burn straight water, and that's why we have systems in place to mitigate how much gets into the system.
Small amounts of water injected into the engine will actually boost performance. Water's heat-absorption properties allow it to (once injected) suck up much of the left-over heat from the engine's previous combustion cycle. This means that the engine is cooled and less work needs to be done to compress the fuel/air mixture. Upon combustion, the water vaporizes and expands much better than dry air, boosting compression greatly. The practice of using water (and often alcohol) in engines is known as Water Injection and has been around for a long time.
However, putting too much water in the engine can over-boost compression, which can result in blown cylinders, cracked pistons, and many other forms of damage. It can also lead to hydro-lock, which is when the expanded water vapor occupies more volume than the cylinder provides. This can at best stall the engine, or at worse blow a cylinder.

I'm not sure I'd say water contamination in fuel is an "over-inflated issue" -- Every year we have a bunch of accidents because some dolt didn't sump their tanks (or "got a little bit of water", tossed it away, and didn't keep draining to look for more).  Having your engine try to burn water 200 feet off the ground in your initial climb can really ruin your flight.

Agreed with Voretaq. Since water sinks to the bottom of the tank, there's a pretty decent chance that it will end up being sent to your engine during takeoff/climb out, which is bad news since engines can't burn water. For significant amounts of water, the water and fuel will separate entirely in the tank, so you won't be getting fuel with a little water, you'll be getting straight water.

Since water is more dense then kerosine, the water will sink to the bottom, where the fuel tank outlet also happens to be, meaning that if there is a sizeable amount, the engine will stop, since there's simply nothing to burn.

Approximate densities of a few fuels:

Water: 1 kg/l
Kerosine: 0.82 kg/l
100LL: 0.72 kg/l

Water mixes with kerosene quite well.

@Articuno: It would be correct for gasoline, but as long as it says kerosine, I believe it is not. At least until there is a lot of water, than it will also gather at the bottom.

The other problem with water contamination is that it can freeze in the fuel lines at high altitude, effectively blocking the fuel line with ice, and preventing the fuel getting through. Fuel treatments such as Liquid Engineering Fuel Set are recommended for preventing water from settling in fuel storage tanks, but not for aviation. This is because the water will still be present in minute particle size,- suspended in the fuel , and burnt in the fuel. But the tiny particles of water can still ice up at sub zero temperature.

Although I would agree that “because of ice” and poor combustion are probably the MOST important reasons, I thought I’d add that water can wreak havoc on many fuel quantity systems.
Most fuel quantity systems are a capacitance style system in which the fuel acts as the dielectric of a capacitor. When water sits at the bottom of the tank, it can cause the dielectric value of the probe(s) to drop to essentially zero. This can cause a myriad of problems ranging from inaccuracies to total system failure.

fuel tank corrosion will also be a problem at the lowest spot in the tank, where the water tends to puddle under the gasoline. This is a very common problem in motorcycles during extended periods of disuse and can actually perforate the fuel tank.


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How meaningful is the total number of flight hours?
What hours count towards the total number of flight hours?
In a long haul flight, do all the hours of the flight count towards the total? Even if the pilot is resting?
Do 10 short flights of 1 hour (that is, 10 times take-off and 10 times landing) count the same as 1 flight of 10 hours (1 take-off, 1 landing)?
Is it possible that two pilots with 1,000 hour have a totally different real flight experience on their back?

Can you say which jurisdiction you're asking about? For example, in the US pilots must log certain times but not others. And 1000 hours in a Cessna 152 are not the same as 1000 in an Airbus A380, but I assume that's obvious :-)

I was wondering this too. I've heard people say "I have 10,000 hours experience in a 747" or whatever, but how much does that matter? I guess for airline operations, it means you've been a 747 pilot for at least 10 years, which is something.

@Pondlife: I wonder for the US/Canada, Europe. And yes, the Cessna/Airbus difference is obvious, like many other qualitative differences between the same amount of hours. However, the question is about differences that do not get logged.

Well that was interesting... no answers for an hour and 3 within about 15 seconds of each other.

And interesting, @reirab, that they are 3 totally different answers. I believe that shows that while this question is too broad to get a good answer, it's an excellent question!

Comparing the number of total hours (on the same plane) you get a fair estimation of how many unusual situations (or emergencies) the pilot may have handled.

As far as what hours are logged, there are a couple of different ways to do the counting.  On a light aircraft, time on the Hobbes meter is generally used, which equates to "engine running" time.  In the military, it's takeoff to landing, usually plus a small amount for taxi time (which may or may not account for all the time that the pilot is actually operating the aircraft).  In the airlines, it's "block to block" time, so pushing back from the gate until stopping at the gate.
As far as the time all being equal, it isn't.  Not even close.  2000 hours flown from Big Airport A to Big Airport B, 8 hours at a shot, means about 125 takeoffs, approaches, and landings flown, and an equal number monitored.  Almost all of those are radar vectors to an ILS approach -- very standard & predictable.  Five hundred hours as a pilot training instructor probably translates into about 500 landings performed, and many, many more supervised, with a great variety of approaches flown (visual, precision, non-precision, practice emergency patterns, etc)  The "hands on" time on the controls of a military fighter pilot in 500 hours logged is far greater than the hands on time during 2000 hour trans-Atlantic airline flying.
The problem is, "hours" is the currency that we have, and so that's how experience is measured.  Not because it's a great measure, but because anything more granular becomes very complicated and subjective.  Does my 1000 hours flying Lear jets count for more than your 1200 hours flying a King Air?  One's a jet, the other a turboprop.  Did one of us fly 3-hour legs mostly on autopilot on clear days, while the other flew 30 minutes at a time, much by hand, with lots of instrument approaches in bad weather?  Who flew with veteran copilots, and who flew with copilots brand new in the airplane?  Who flew to lots of unfamiliar destinations, and who flew the same canned route(s) day after day?  And how does any of that compare with 3000 hours in a C-5?  Or 800 hours in a crop duster?
All of this to say, that "hours is hours", while it overlooks a LOT of very relevant distinctions between some very diverse types of flying, is still the quick and easy comparison between pilots.  Not because it's wonderfully accurate, but because it's possible (we all log hours, after all), and the more detailed comparisons quickly become hard to objectively make.

Yes, regarding the training issue, when practicing landings, an hour of training can equate to 8 or so landings... and essentially no navigation at all (unless looking to your left and seeing "yep, there's the runway" counts as navigation.)

I believe that you meant the Hobbs meter. Calvin's friend has nothing to do with it that I know of. :-)

I don't fully understand what you're asking, but here's an attempt to cover the main interpretations (as I see them) from a US perspective:

When a pilot says "I have 1000 hours", where does that number come from?
Pilots have to log their flight time for various reasons (see this question and the logging tag), some legal and some personal. It's a fairly safe bet that anyone with more than - let's say - one hundred hours has flown more than that, at least for some definition of "flown". One key number is PIC time, i.e. the time that the pilot was legally responsible for the flight, but there are different practices and legal requirements so the numbers will never be consistent between pilots. And a private pilot who 'only' flies his family around in a Cessna 182 will end up with different logged time from a professional pilot who flies an A380 with hundreds of passengers, even if both have spent roughly the same number of hours "at the controls" (which isn't clearly defined anyway).

What time do airline pilots count towards their 'total'?
This depends on who's counting. The people who care are the FAA (or other authorities) for legal currency and training purposes; the airline (i.e. employer) for pay, seniority and scheduling reasons; and the insurance companies for coverage. All these people will have different views of what "time" means, although PIC time is usually the most fundamental measure. But in airline operations especially, SIC is also well-defined and important.

When two pilots say "I have 1000 hours in A320s" (or whatever), do they have the same level of skill and experience?
This is impossible to answer. Take two 30 year-old American men (for example) from the same state who have been driving the same make and model of car every day since they were 16 with no accidents or police tickets. Are they equally good drivers or not? Legally speaking yes: they have the same licenses, background and driving record. But most people would agree from personal experience that they know of a "lucky driver" who has avoided police trouble for years despite driving riskily. Fortunately pilots are more strictly regulated than drivers and the flight and medical checks are much more frequent, so the differences are correspondingly smaller.

Of course I'm completely ignoring the operational experiences, e.g. a pilot who flies between JFK and Atlanta every day will accumulate different experience from one who flies between JFK and Podunk. And does Sully's experience make him different from someone else with exactly the same number of PIC hours in the same aircraft models but who didn't land in the Hudson?
I have the feeling that you're trying to ask if someone with more hours is generally a 'safer' or 'better' pilot (I may be completely wrong about this). If so, the short answer is no: it's impossible to compare two people's experiences directly anyway, and it's commonly said in aviation that it's better to fly 1,000 different hours than to fly the same hour 1,000 times. This applies to many other areas of life too :-)

I like your last sentence: it's better to fly 1,000 different hours than to fly the same hour 1,000 times

@kevin Don't get married then xD

For the United States, the relevant regulation is 14 CFR 61.51, which defines requirements for pilot logbook entries. In general, hours will be logged as one of the following categories:

Pilot-in-Command
Second-in-Command
Training (i.e. Instruction Received)

Student pilots will log either as Training when flying with an instructor or as pilot-in-command when flying solo. Non-student pilots will log either pilot-in-command (when the Captain or the only pilot) or second-in-command (when acting as First Officer.) For purposes of total hours, all of the above are included.
Apart from the above categories, hours flown solo, in instrument flight conditions, and at night are tracked separately. These factors don't have any bearing on your total hours, but do matter for satisfying pilot certificate eligibility or currency requirements.Flight cycles (number of landings and takeoffs) don't matter in terms of total hours, but number of landings is also logged as a separate parameter.
14 CFR 61.51(e) says the following regarding what can be logged as pilot-in-command time:

(e) Logging pilot-in-command flight time. (1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-
(i) When the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;
(ii) When the pilot is the sole occupant in the aircraft;
(iii) When the pilot, except for a holder of a sport or recreational pilot certificate, acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted; or
(iv) When the pilot performs the duties of pilot in command while under the supervision of a qualified pilot in command

As far as whether rest time counts when operating long-haul flights, I wasn't able to find a definitive answer. The regulations in 14 CFR 61.51 don't seem to be terribly clear on that point. Even reading what actual pilots flying such flights have done seems to show that different pilots have handled it different ways with some logging all of the hours, some logging only when they were 'in the seat,' and others logging a given fraction of the flight time (e.g. logging 2/3 of the time on a 3-man crew where one rotates out to rest.) Perhaps one of our pilots with long-haul experience around here can provide more insight on this.
As far as the title question of how 'meaningful' the total hours are, that's a rather subjective question on which different people will have different opinions. Regarding your last question, certainly not every 1,000 hour pilot will have exactly equal experience, but how different their experience may be will vary quite a lot between any given set of two 1,000 hour pilots. It's entirely possible to be a 1,000 hour pilot without ever having sat in a powered airplane (by flying gliders, helicopters, etc.,) for instance.

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Do airplanes need wings?
Couldn't you just generate lift with a long body? Maybe a little broader than a normal plane.
As a design enhancement, we would need  a heavier bottom, so the plane doesn't flips to a side.

fighters are designed almost like that or flying wings

Related, even though the designs still had regular wings: http://aviation.stackexchange.com/questions/3842/disadvantages-of-early-prop-driven-blended-wing-aircraft

lifting bodies that helped developing the space shuttle hardly has wings

Do airplanes need wings?

Wait a minute! Airplanes have to have wings by FAA regulation, so you won't find any airplane without wings in the US.
FAA definition:

Airplane. An engine-driven fixed-wing aircraft heavier than air, that
  is supported in flight by the dynamic reaction of the air against its
  wings.

My advice here: If you encounter an airplane without wings (an unapproved case) do only your duty, call FAA immediately at 866-TELL-FAA (866-835-5322):

(Source)

Aircraft on the other hand has benefited from FAA's leniency, and don't have to have wings:

Aircraft. A device that is used or intended to be used for flight in
  the air.

As you can see, they are not required to have an engine, nor large rocks in the cargo hold to ensure they are still heavier than air. No, the only requirements for an aircraft are that:

At the beginning you intend to make the thing fly. It's perfectly legal to try to see if you could save wings from the bill, as long as you are honestly expecting it to fly.
You want it to fly in the air, not in the water, certainly not in the vacuum of the space. That's the part requiring all your attention during the design. The lift must be carefully monitored, you need to remain in this tiny layer called atmosphere, else you leave the aircraft category, and maybe the aviation field too.

This is a wingless aircraft:

Full scale Lippisch's Aerodyne, a VTOL aircraft built at Collins (Source)
This one is fully in the law, don't call FAA...

It's certainly a stupid answer, I did my best for, but it's correct :-)

He has a point.

You get +100 pedant points. Nice work!

The "aircraft" definition doesn't require that it has to be only used for (or be intended for) flight in the air. The Space Shuttle certainly was intended for flight in the air, even though it didn't remain in the atmosphere.

@cpast: Interesting! According to Wikipedia the Space Shuttle was a spaceplane: "an aerospace vehicle that operates as an aircraft in Earth's atmosphere, as well as a spacecraft when it is in space". It seems they have anticipated all cases :-)

Yes you can, these are called lifting bodies, they are not very efficient and require a lot of speed before they generate enough lift to stay aloft, requiring a long runway.
In 1983 a F-15 fighter lost a wing in a mid air collision and was able to land safely due in part by the main body being able to generate enough lift for the plane to stay controllable.
They are only really useful for supersonic flight where normal wings create too much drag

That f-15 story never fails to amaze me.

Saw a pic of that F-15. A couple feet beyond the wing root the wing was just ... gone. Amazing.

Pics or it didn't happen: http://skeptics.stackexchange.com/questions/9884/did-an-f-15-airplane-successfully-land-with-just-one-wing

Although remember that the F-15 also has a >1 Thrust-weight ratio... in theory, if you could balance one properly, you could pull up vertically and reduce power which would allow could hover and land vertically on the tail. In that crash, the engine thrust was used to augment lift (along with the high speed)

There are indeed lifting bodies which were able to fly without wings. But wings are much better at creating lift than a bulky fuselage. The space shuttle was developed based on testing lifting bodies, which allows it to have fairly small wings.
What you are describing sounds a bit like the blended-wing-body (BWB), which smoothly integrates the fuselage with the wing. Sort of like a commercial version of the B-2 flying wing design.

This is certainly still in the concept phase. Boeing has flown a scale model to test the concept, and it has performed well. Aside from being more efficient than traditional designs, it can also produce much less noise if the engines are positioned above the fuselage.
We have about 100 years of development in the traditional airplane design, which contributes to the efficiency and safety that we are able to achieve right now. Going with a BWB design alters so many of the standard design features that this presents a very radical change. When the benefits start to outweigh the costs of moving to this design, we may start to see more planes like this.

The BWB design is interesting, but it's unlikely to ever be used in an airliner.  First, this shape doesn't fit nicely into the gate systems at airports.  Second, most of the passengers would have to sit too far from doors or windows to be comfortable (or to meet evacuation requirements).

@fluffysheap yeah, waaaay too many middle seats in a plane like that.  It is interesting how much customer perception matters. I remember watching a documentary on Boeing vs. Lockheed designing a new fighter (Lockheed won and gave us the F-35), but Boeing's design was so radical, it almost was doomed from the beginning because it didn't "look" like what a fighter "should" look like.  I think the same thing applies with airplanes. In fact (and this is ridiculous), I knew someone who wanted to fly Pipers rather than Cessna singles because the Pipers "looked like a real airplane."

Hey! More radical and absurd airplane designs: http://www.dailymail.co.uk/sciencetech/article-2538651/The-future-air-travel-Three-storey-Sky-Whale-fits-755-passengers-virtual-reality-windows-self-healing-wings.html

Saying that lifting bodies testing is what allowed the shuttle to have small wings might be a little misleading because you make it sound like the shuttle was designed using lifting body concepts, when really all they shared in common was a steep approach profile followed by a long flare. In fact, one of the reasons lifting-body research was abandoned by the US Air Force was because the Shuttle decided to go with a double-delta wing instead of a lifting body configuration.

Yes it is possible but the lift needed to lift it off the ground would be so incredible. There was one prototype plane produced by the USAF on this design. The plane was the NASA M2-F1 and it was incredible for the time. It was 20ft long and 9ft 6in tall. It had a bodyspan of 14ft 2in. The theory worked  but the problem was it ran on solid rocket fuel. This resulted in a large engine and a even larger fuel cost. It only could go about 130 knots and that was on full throttle. It also only had a range of ten miles.... Yeah.
So as you can see yes this was a idea and the theory is there but we need some much better engines before it becomes practical.

I do not know about other airplanes, but, I can say that you can remove the wings on a Yack RC aerobatic plane and make a take off, climb to altitude, level off and perform level flight, perform barrel rolls. inside loops, Cuban 8s, and perform high rate rolls. Last you can land the plane safely. All this demonstrated on RealFlight Simulator.
There are some techniques not normally used in winged flight that must be understood and used to make this wingless flight possible.
(1) The prop's pulling vector must be high enough above level to the ground so that the lift component of the vector is larger quantity than the weight of the fuselage. Remember, the plane is very light as there are no wings.  Fuselages could be built much lighter as there is no wing stress on the fuselage, and the maneuvers, excluding high rate rolls, are slow rate of turn and pitch attitude meaning g forces are much smaller and insignificant. Pulling out of a loop at the bottom is made possible by the tail pushing the back of the fuselage downward which raises the nose upward and causes the tail to fly below the axis of flight. Some of the lift for the pull up is distributed along the hull of the aircraft as wind hitting the bottom of the aircraft creates lift. This lift distribution along the entire fuselage distributes pull up g forces along the entire fuselage. Net very low g force concentration. The center of lift of a wing is outboard of the fuselage, the outboard location causing a bending moment on the wing at the attachment to the fuselage.  This creates a wing breaking stress under high g forces. Also, the stress is at the point of attachment of the wing and this stress is countered by the weight of the fuselage which is distributed in front of and behind. The fuselage thus must resist the front to back centralized stress to resist breaking up at the wing junction. No such problem with the wingless aircraft.
(2) With no wings to add weight, the wingless plane can take off in very short space.  The taller the landing gear (assuming a tail dragger design) the higher the angle of incidence of the fuselage and axis of propeller pull.  Building taller and taller main landing gear allows the plane to take off in shorter and shorter distances to the point where if the axis of the fuselage was straight up, the plane would take off straight up. With no wing weight, the plane would climb very quickly.
(3) Until the plane's wheels leave the ground, the prop's wash and its axis of pull is in line with the fuselage, the wash hitting the elevator and rudder, the rudder's upper part above the prop's axis. Right rudder turns the plane on the ground to the right but being above the fuselage axis, right rudder also induces left roll. This roll is against the turn and causes to be vary unstable, the plane susceptible to simply rolling over on its side if the width of the landing gear is not enough to counter the roll vector. It is suggested that a wingless plane have wide landing gear for this reason.
(4) Once the wingless plane leaves the ground, the nose initially rises while the tail is still on the ground.  This makes a steeper angle of the fuselage to the plane's direction and the prop wash (as seen when a smoke screen is used on the front of the fuselage) completely misses the tail sections, the wash flying over them.  The axis of roll of the plane is concentric with the prop wash. Now, when the rudder is turned to the right, the vector of the rudder turns the plane to the right on the direction of flight axis.  However when turning right, the rudder being below the axis of roll, induces a roll moment on the axis of flight that roles the plane to the right. In this nose up fuselage angled below the axis of flight, the rudder performs the turning function and the roll function. If the flight speed is too fast, the axis of flight and the fuselage axis close together and the rudder behave in turn in a direction opposite the rudder input. This flying with the nose too low causes loss of control and can result in extremely fast roll rates. It thus becomes  paramount that the wingless plane be flown with very high nose up attitude. In level flight the speed building up will start leveling the fuselage and result in loss of control and stability. To counter this leveling off as speed builds up, simply lower the power setting.  This also means that the wingless plane will not straight up as the fuselage angle to flight angle will be 0 and the rudder will cause loss of control.  At the top of an inside loop, the tail will pull the tail over the top maintaining the rudder's roll and turn function.
(5) Turning:  The rudder in nose high attitude will swing the nose but it will also bank the plane. Initiating right rudder  will bank the wingless plane to the right. At this time, the operator simply pulls back on the elevator which causes the plane to turn similar to a winged plane, a coordinated efficient turn.
(6) Landing: A few prayers help! To lose altitude don't push the nose down with the elevator as this will cause the tail to rise up onto the prop wash creating instability and loss of control. Rather, pull back on the power maintaining full up elevator. the plane will sink at your desired speed. The plane will appear to hit hard on touchdown, but the front wheels and the tail wheel hit together or tail wheel first absorbing impact. Also, remember that the weight of the wings is absent. The plane can land at a very high sink rate without destruction of landing gear or broken fuselage.  I have broken many main landing gears landing planes hard with wings. To date, I have not broken one landing gear landing many times wingless. Remember, when landing with no wings that the moment the tail and mains are on the ground, the prop wash and axis of flight are level with the rudder and the plane is prone to tipping over when rudder is actuated. Use rudder judiciously until the rolling speed has slowed down.
(7)I suggest that all aerobatic airplane have split control on the elevator. The elevator is in the prop wash and is effective in slow speed nose high flight. When right aileron is initiated, the elevator's right side will turn down slightly and the left side will turn up.  This splitting could be done by putting separate servo controls on each independent side of the elevator or 2 the push-pull control servos could be run to each side of the elevator but the servos could be on attached to each other and a third servo could pull the two servos to actuate elevator function. This would give back to the airplane's operator the ability to control bank, the bank not dependent on being below the airflow of the prop and axis of flight direction of the flight.
Can the plane perform in the real world with the above modifications?  I believe so. Wingless flight with split elevator would open a complete new world to freestyle RC flight. Wings could be made to be easily removable before takeoff or could be made  to be dropped off during flight. Pilots could develop no wing flying skills using the RealFlight Simulators, the skills developed  while going through the inevitable crashes without having to rebuild expensive equipment.  Just hit the reset button!
Bottom line, the answer is a surprising YES!
Below is 17 minute YouTube video I published with aerobatics and without wings:

This answer could be improved by using something more realistic than RealFlight, and with a video using screen capture instead of filming the computer screen. But it is an interesting discussion of the physics involved. The observations here seem mostly limited to the RC scale though.

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text:
Could a commercial plane seat configuration look like a troop carrier?
I wonder whether Michael O'Leary has already seen that. I am pretty sure he would be eager to implement the idea. However, is that feasible - both from a legal, and as a security policy - for commercial planes transporting civilians? Maybe military personnel can be trusted to evacuate the plane faster than average civilians in case of emergency.

Source: dailymail.co.uk

I think it's more that military transport isn't held to the same rules because soldiers signed a waiver about that.

Side-facing seats must comply with the regulation made for the aft/forward facing seats (14 CFR part 25 for the US). I doubt the survivability tests would be passed.

Related: Special Conditions: Boeing Model 787-9, Dynamic Test Requirements for Single-Occupant Oblique (Side-Facing) Seats With Airbag Devices

Related: Neck Injury Criteria for Occupants of Sideward Facing Aircraft Seats (Mat Philippens).

Without an indication of the type of plane or dimensions, it's difficult to judge it this is actually more packed than some currently existing civilian airliner configurations. Not sure the soldiers sitting sideways actually saves any space (though most seem to have their rucksacks at their feet rather than in the non-existing overhead luggage lockers). The main different I see is the lack of any space for galleys, restrooms, etc.

I believe the apparent lack of space or the discomfort is a red-herring. That's simply not the case.
The passengers don't seem to be tighter packed than in a Ryanair flight actually. And I also don't believe that the sidewards configuration is motivated by this rationale.
The aircraft is a Boeing C-17. It does not have a civilian version, so direct comparison of seat arrangements is not possible. Its inner space, however, is actually 18 feet (5.49 m) wide for 7 passengers and two ailes. So, it appears that the latter is less generous with its 737-800 < 12 feet wide with a single aisle, for 6 passengers (each getting 17.2).
The Boeing C-17 is a multi-purpose military aircraft, designed to be adapted to different tasks (hence the sidewards seat).
It is meant for being used for medical evacuation:

Or, for transporting a howitzer:

Or, for transporting paratroopers:

The sideways configuration appears to be simply because those seats are built-in (note that they are visible on all the images, possibly folded).

@JanHudec: yes, it appears that they keep the side seats in all configurations, and they can be folded out of the way.

Legally, you would need to find a seat that passed the FAA's 16 G "side facing" requirements. The AC that covers the 16G rule has some text that may be of interest on this matter. The FAA admits that its an ongoing area of research and that currently special tests need to be undertaken to certify one. (bolded for emphasis)

d. Side-facing Seats.
(1) General. All seats occupiable for takeoff and landing are subject
  to the specified dynamic test conditions. Included are side-facing
  seats and both single occupancy and multiple place seats, such as
  divans. Compliance with the structural requirements should be
  demonstrated for side-facing seats, using the same conditions for the
  test and pass/fail criteria as for fore- and aft-facing seats. The
  seat should be loaded in the most critical case structurally. Means of
  restraining the ATDs may need to be adapted to ensure adequate
  retention during the test. The application of floor distortion will
  need to be assessed on an individual basis, depending on the design of
  the fixation of the seat. The injury criteria of § 25.562 are not
  adequate to demonstrate equivalent safety of side-facing seats when
  compared to fore- and aft-facing seats. To demonstrate equivalent
  safety fully in the absence of such specified criteria, the applicant
  must use other injury criteria which may be derived from the
  automotive industry, which uses side-impact ATDs.
(2) Assessment
  criteria. Research into side-facing seats is ongoing. As research
  proceeds, the FAA will work toward establishing a more definitive
  policy with respect to the acceptance of side-facing seats. Until
  then, in the absence of specific compliance guidance, the FAA is
  prepared to assess side-facing seats on the following basis:
(a) The
  seat must demonstrate compliance with the structural requirement.
(b)
  If an acceptable side impact ATD has not been used with assessment of
  the corresponding injury criteria, it must be shown that the occupants
  are restrained in a manner that prevents substantial energy absorption
  by body to body contact (on a multiple occupancy seat) and which,
  using the best available engineering judgment, minimizes injury to the
  occupant(s).

The way this reads in short (at least to me) is that the FAA does not really test side facing seats all that often but they are willing to if an appropriate means of testing is devised, you can prove that people smashing into each other wont cause any serious problems and that your seats will be ok when a shock wave passes through the floor (same as the forward/aft facing seats).
The FAA also has an extra supplement for potential injury from side seat configurations thats worth taking a read through "Supplemental Injury Risk Considerations for Aircraft Side-Facing Seat Certification"

On the evacuation note the FAA does not really care what the seat orientation is in terms of evacuation. If you are talking about converting a modern airframe you likely could not place a seat in front of the over wing exits but other than that so long as you comply with the evacuation time limits you will be good to go (from a strictly certification stand point). Since this configuration still has rows similar to that of a normal airliner I dont see why you would not be able to properly demonstrate evacuation capacity in this configuration.

The biggest issue I see here is a lot of toes getting run over, and knees bashed by a galley carts...

Don't compare military troops transports and airliners.
Goals are not the same, inducing requirements and means differ. Not to say that soldiers can be packed as cargo, but military transports are supposed to mobilize huge amount of troops with their equipements on the battle field in no time, and soldiers know that and are prepared for critical scenarios.
If troops were to ask for same treatment as civilian passengers, it would raise the following issues :

you'll need wider seats and pitching, in a more "civilian" configuration, meaning much less "passengers" per aircraft, and much less troops carried per flight.
more planes to carry troops, more targets for the enemy. You don't always fly in ally airspace.
This increases aircraft operations, which kills one military strategy called sneak attack. Predictible operations are a strategy error.
More flights means more time to be handled, meaning delays. Time is always an issue in military operations, both upon mobilizing, and returning back home with waiting families.
if you want to have both nice seatings and paradrop capabilities, you'll have to make room for the drop process which also removes more seatings.
optionally, you'll also need flight attendants to serve meals.
All that induce more costs (planes, civilian plane equipements like expensive seats, galleys and trolleys, etc.) which increases military budget.

It seems on a military point of view, having civilian-like things doesn't bring advantages, only issues. So that's how it is.

If troop transport concepts were to be used on civilian side (airliners), I don't think you and me would agree (assuming we're not soldiers)

we paid for the flight, soldiers are paid to fight and signed with all that comes with that duty including death.
we just want to have a good flight from departure to destination in the safest possible way, in a comfortable seat, with meals and entertainment.
if airliners were that "loaded", we'll have less flights per route, meaning less schedules. If the schedule doesn't comply with your plans, you'll have to wait for the next available flight.
serving meals would be much more complicated; perhaps it's better to have lunch before flight, not inflight. Ask a flight attendant's opinion about serving meals and pillows in that condition...
lavatories on the other hand would always be mandatory, don't worry. But we should be trained to walk through, step over sleeping passengers legs...
we would have to sign a waiver about the sideward facing neck (head, and shoulder) injury(es) in case of critical stop.
we would also have to sign a waiver about "flying bags" upon turbulences. It's highly unlikely you would be able to put everything in luggage bins with that much passengers in a Boeing 737.
The only advantage would be a substantial reduction in travel cost (on our side)

Worth it ? I, personally say NO !

By the way, mass evacuations are a huge step beyound your posted picture. ;)
I inverted scenarios by suggesting why military personnel wouldn't have the same treatment as civilian travelers on purpose : you're comparing two very different situations that doesn't have the same priorities, goals and safety concerns. That means what matters, what is more efficient, what costs less in a case are not the same for the other. The target audience is different. One is going to fight at war, the other is on vacation/family/friends visit, business travel or starting a new life. That means it's not only about safety concerns.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What makes a jet single pilot certified?
Why are some small-ish jets (Embraer Phenom 300, Pilatus PC-24 for example) single-pilot certified? The pilot still has to fly+navigate+communicate. Why would a small jet be more manageable than a bigger jet? Or is it more the case that they would not kill as many people if things go belly up?

According to this blog:

Up until 1977, the FAA required all jets to be operated by two pilots. In ‘77, Cessna was given approval on a single-pilot variant of the Citation I, the Citation I-SP. The aircraft met the 12,500-pound maximum takeoff weight threshold for small aircraft, but that wasn’t the only single-pilot qualification. Cessna also had to convince the FAA that its pilot workload was low enough for one pilot to handle safely.
According to J. Mac McClellan with Flying Mag, in order for an aircraft to qualify for single-pilot certification in the 70s, “you had to have a boom microphone for hands-free communications-somewhat uncommon 30 years ago-and a fully functioning autopilot. There was also the quaint requirement for a transponder ident button to be mounted on the control wheel. In those days, we would ident on almost every controller handoff.”
One of the most important (and obvious) requirements for single-pilot certification of an aircraft is the fact that all gears and controls must be accessible from the left seat. The autopilot must be seamlessly integrated into the airplane’s navigation systems, and it must be functional for every flight operated by one pilot. The aircraft must have hands-free communication, as well. Aside from those concrete requirements, the rest is subjective.
After a series of test flights, the FAA’s test pilots must come to the conclusion that the aircraft is safe for a single pilot to fly. The design of the aircraft’s controls is one of the most important factors, as one pilot must be able to operate the throttle, the yoke, control wheel, and other flight controls easily from the left seat.

So, all of the aircraft's controls must be operable from the left seat, there must be hands-free communication, and an integrated autopilot.
Now, of course, there is also a single-pilot type pilot's certification, which a pilot can obtain to legally fly aircraft which meet all of the requirements above, yet are larger than the 12,500-pound maximum takeoff weight threshold.

Does the auto pilot need to be functional even under VFR and/or VMC operations?  (Granted most jets will get into class A, and therefore rarely operate VFR, but our operating certificate for the Caravan only required the AP to be functional for IMC)

@MichaelHall Don’t forget the requirement for a working autopilot to fly in RVSM airspace, which nearly all jet flights will do.

When I was flying CRJs I had ready access to a simulator that I could use in visuals-only non-motion mode (bridge down, door open) when it was free, and used to spend a lot of time practicing flying it alone.  Beyond having to reach for things, the flying itself wasn't an issue and I knew I'd have no problem flying alone if necessary (if it wasn't for the nosewheel steering, it would have been more convenient to fly from the right seat).  The real issue is overall mental IFR workload and the lack of CRM benefits, which when done right, makes 2 heads much safer than 1.

@StephenS Air transport jets. There are jets for other purposes. Like VFR flights in a trainer like L-29. I doubt  the plane can do RVSM in the original config.

Pretty sure that there were single-seat fighter jets prior to 1977.

AIUI in the US the military is not under the jurisdiction of the FAA.

authors: Vladimir F Героям слава


text:
How do intake deflectors work?
Some turboprop aircraft, for example DHC 6 Twin Otter have “intake deflectors” which should be engaged when taking off from or landing on unpaved surface to prevent foreign object damage. But how does it actually work?

First hit on Google: http://airplanepilot.blogspot.fi/2005/06/intake-deflectors.html

@VilleNiemi second hit on google: http://aviation.stackexchange.com/questions/16206/how-do-intake-deflectors-work , and that one has illustrations too! ;)

@falstro I have to say I am impressed by the google fu of the stackexchange. This probably isn't that common a search term, but still...

This document describes it nicely. They are also known as inertial seperators:

The nacelle inlet of many aircraft models includes an inertial separator
  provided by the aircraft manufacturer to prevent heavy particles from
  entering the engine inlet. Most installations incorporate two moveable
  vanes, one upstream of the engine inlet and the other blocking the bypass
  duct. For bypass operation, the inlet vane is lowered and the bypass
  duct vane is opened permitting maximum separating efficiency. In some
  installations, the vanes are fixed in the bypass mode.
As shown in the sketch, air entering the engine inlet must turn sharply past the inlet vane (shown in the lowered position). Particles heavier than air are carried straight through, by their own inertia, into the bypass duct and dumped overboard.
The aft radial inlet design provides many advantages such as superior
  anti-icing utilizing the principle of inertial separation, low noise levels and unequalled protection from FOD.


text:
What is the material of the wing spar on the Mitsubishi MU-2?
I read that the spar on Twin Commanders are made of steel. Is this also the case for the MU-2?

According to Jane's all the world aircraft only the "main spar caps" are made "of heat-treated SAE 4000 series stell". For the MU-2 it gives 2025 and 7075 aluminium alloy as materials used for the wing.


text:
What's are the advantages of having the pilot in the cockpit?
Instead of a pilot in the cockpit, how far are we from having commercial airplanes with remote pilots (like drones)?

The remote pilot won't have any kind of space disorientation
Each of its actions would be scrutinized in real-time
pilot could be swapped every t time, so you'd always have a rested pilot
less costs, all remote pilots could have a 9-17 type of work. The airlines would just pick one in the matching time zone
the cockpit could be converted into a 1st A class space

Is there any situation where the pilot needs to feel the airplane, maybe not to override the information from instruments, but to complement it?
I'm aware that this might be a big no-no for some passengers, but how far are we of implementing this in a cargo airplane?

Related: Could the CVR and FDR record to the cloud?. Aircraft sending flight data to the ground would be a prerequisite for controlling it from the ground.

"The remote pilot won't have any kind of space disorientation" neither will they have any situational awareness. Piloting drones has been occasionally likened to "looking through a straw".

Remote pilots certainly would have spatial disorientation.  And what happens to the remotely-piloted airplane when the communication fails?  While I'm not entirely sure about e.g. transoceanic airline flights, there's a lot of airspace in the US west where a light aircraft has no radio contact with ATC.

The concept would be a hard sell for both passengers and non-passengers alike. You not only risk lives in the air, but on the ground as well. I would not want a fully laden B747 flying above me. The biggest reasons are:
The human pilot in the cockpit has a vested interest in performing a safe flight. The vast majority of pilots are not suicidal (99.999%). The remote pilot on the ground does not have the same incentive.
Any computer system can be hacked. This would turn said B747 into a weapon. A terrorist attack similar to 9/11 would not have to be a suicide attack, removing a major deterrent to such attacks.
A remote pilot does not significantly lessen the chances of human error. The remote pilots are still human. And, the programmers of the software needed to make remote piloting possible are equally human.
Satellite communication is not entirely fool-proof. It would have to be perfect to be considered safe enough to warrant that hazard. The current GPS interference is an example of that. That is one of the reasons why GPS is still considered non-precision for flight. You have to have the capability to use traditional NavAids even when you are using GPS.
When (not if) crap hits the fan (or fan disk), and there is a systems failure, the best chances to preserve life is to have the human pilot in direct control. Think of what happens in an electrically power failure, a systems shutdown, a loss of communications capabilities, etc.

"A terrorist attack similar to 9/11 would not have to be a suicide attack, removing a major deterrent to such attacks.", I'm not sure suicide is a major deterrent for those willing to undertake this kind of terroristic activities


text:
How criminal is it to take off without authorization?
In the US, how would someone like the Seattle guy be punished (that is, plane heist without passengers, unauthorized take-off and midair stunts ) if he hypothetically had not died, but landed the plane intact?
Background story: Richard Russell, Who Stole Plane Near Seattle

I'm sorry, but I don't see how this is on topic here. I'll wait for others, but my feeling is that this is a law.SE question.

@Federico: the question could be read as 'how criminal is it to disregard ATC?' I think it will get a more detailed answer here, although yeah, I suppose only a small group of people would need to know an answer to this.

Well, I see your point. Mine is that if you are asking "how criminal it is", you are not asking about FAA rules, since they are not part of criminal law, afaik. So if you are asking "what would happen if that guy would have ended up in court", we can't really answer that here. If the question is instead "what happens to your licence", well, see Ron's answer below.

The FAA has limited ability to enforce criminal actions for non-compliance with FAR's. Essentially the pilot (certificated or not) would be subject to either Informal Procedures/Settlements, Certificate Actions, or Civil Penalty.
The FAA's policies, procedures, and guidelines are located in the FAA Compliance and Enforcement Program, Order 2150.3B.
In the case of stealing an aircraft by a non-certificated individual, the only recourse the FAA would have is civil penalties. The authority for the FAA is located in 14 CFR 13.14 or 13.18. The FAA has the authority to issue civil penalties up to \$400,000 against "persons other than individuals and small business concerns" (aka large businesses) or for individuals and small businesses up to $50,000.
In the case of the stolen aircraft, the charges would probably be theft and whatever other federal/local charges could be levied, but the FAA would probably not intervene here.
Teen aircraft thief sentenced to 13 months in prison (60 days served)
Felony theft charges for stealing airplane
Barefoot Bandit
It isn't strictly "illegal" to disobey an ATC "order". A PIC (supposing they are a licensed pilot) can disregard ATC if they feel that the safety of the flight would be in jeopardy if the order was followed. Specifically this is allowed by JO 7110.65W, page 3-3-1 and 14 CFR 91.123.

I wonder if the EPA would also have something to say if you crashed an aircraft deliberately, and the National Parks administration if you crashed it into a national park of forest. The legal morass would be incredible, given the number of alphabet agencies that might get involved.

@jwenting I doubt it, given that the perpetrator is deceased, pretty much for the same reason we don't drag deceased people through courts. With the situation that the OP posted I think this is just between the FBI and FAA, maybe with the NTSB assisting. I've never heard of the EPA getting involved in a crash even when a lot of fuel is dumped into the water.

I was talking in general, not about this specific case. Though they could always go after the next of kin or the owners of he aircraft of course. In an accident I doubt anyone would try to sue over environmental damage, but this was a deliberate crash, who knows what someone with his head bolted on wrong comes up with?

@jwenting Unless the person is a minor, the "next of kin" and aircraft owner can't be held liable for criminal acts of another individual unless they are legal guardians. It would be analogous to having your car stolen and then being involved in a crash, the other party can't hold you liable for that.

the government often has powers far beyond what mere citizens have. I've been held responsible for the failure of my employer to pay taxes and social security premiums after that company folded for example. The banks they had loans with didn't get to claim a penny from me, nor did other companies they had outstanding bills with.

That's different though, taxes are paid by the company on your behalf, it is still your debt (even the employer contribution). If you had died, without an estate, they would not be able to collect that debt from your parents, children, or siblings.


text:
Selling the emergency exit row seats
The seats leading to an emergency exit normally offer more legroom and, therefore, the airline can cash a fee for them.
But, shouldn't they pick passengers that would have the higher chance of being able to open the door in case of an emergency?

Well they usually cover that in a pre-flight briefing and brief interviews with the crew asking if they meet the physical strength requirements and are willing to operate the exit door in case of emergencies.

@CarloFelicione Additionally, if you select your seat online, all of the airlines I've dealt with show you the requirements for sitting in an exit row and ask you to confirm that you meet them before allowing you to select an exit row seat, even if you do pay for it.

They do.
If you are clearly not physically able, they will change your seat during check-in.
Then, as part of the safety briefing, you will be explicitly asked if your are willing and able to carry out the relevant instructions.  If you are not, the crew has the authority to re-seat you.
If all passengers are seated, and no-one is in the exit row, the crew will re-seat a capable person next to the door.
Here's but one reference to the requirements from the UK CAA.

Do the passengers get the fee refunded? Or is it their fault, since they should have known better?

I've seen airline companies charging more for seats that offer more legroom, including the emergency exit rows.
One thing to notice is that you only get to pay a fee if you chose your seats by yourself (i.e. when checking-in online). You should not have to pay any extra fee if the only remaining seats are on the emergency exit, either by checking-in online or at the baggage drop-off.
And finally, if you're not willing to take the responsibility when a flight attendent asks you, or if the flight attendent judges that you're not physically able to operate the emergency exit door, they can re-seat you prior take off.
Hope this helps!


text:
Did the XF-84H Thunderscreech really cause "900 sonic booms per minute"?
The Republic XF-84H, known as the "Thunderscreech" was an experimental version of the F-84F Thunderstreak. It was intended to be a supersonic turboprop fighter.  Even at idle, the prop tips rotated at supersonic speeds and the plane is often claimed to be the loudest ever built, supposedly audible 25 miles away.
Most sources describe a continuous sonic boom due to the supersonic prop tips. However, a fairly common claim on the internet is that they caused "900 sonic booms per minute."
Is there any truth to the claim that the plane caused 900 sonic booms per minute?
One's first thought should be, "no": because the prop tips are continuously above the speed of sound, they emit a continuous sonic boom (as most sources claim), not 900 separate ones per minute.  However, since the prop tips were supersonic and the roots were not, it follows that a section of the prop's length would be in the transonic range. Any change to the wind or propeller RPM would cause more or less of the propeller to be moving supersonically.  I suppose that, say, an appropriate oscillation in the turbine engine could cause the continuous boom to be modulated by some 15Hz (900-per-minute) component.

I think it is a matter of where you stand (literally).
From the front or the rear the shock waves from the propeller tips would hit your ears continuously, and the result would be constant noise.
When standing laterally, the propeller tips would move towards and away from you and produce a variation of noise intensity of the frequency produced by the product of propeller RPM and blade count.
It seems that the design RPM of the XF-84H propeller was 3000, and since the propeller had three blades, the frequency should have been 9000 per minute, not 900. The airframe could be split ahead of the cockpit to allow the installation of several nose sections with their own gearbox and propeller. Several gearboxes and propellers were prepared with propeller design speeds between 2100 RPM and 3000 RPM, but the test program was ended prematurely, so most of the planned variations were never flown.
I can only judge from the little information available online and count myself lucky not to have witnessed a power-up of the XF-84H (for me personally, the loudest aircraft is still a Sukhoi 22M-4 – you think "man, this afterburner is loud!" and only then the pilot switches the afterburner on), and it seems that the 900 per minute figure must have lost a zero on its way of becoming an internet meme.
Note that I only speak of a variation of noise – as Jon Story writes, a sonic boom is what arrives at your ear, not what is produced by the propeller.

You get the +1, this was what I was going to say! (I was going to say what Peter said????  Wow, I've learned a lot... )

Are you sure you heard Su-17? AFAIK, Su-17 has never been exported outside of USSR. Its export version was Su-22, and its main difference was a different engine: R-29B (from MiG-23) instead of AL-21F. Only the last version, Su-22M4, had the original AL-21F engine (though it was fairly common).

@Zeus: At the time, I was told it was a Su-17. I now looked into it and indeed it must have been a Su-22M-4. Still the loudest I ever experienced, though.

The 900 probably comes from the idle rpm of the prop.

No, because that isn't how it works
A plane doesn't 'make' sonic booms, a sonic boom is the result of an aircraft overtaking the sound it is making, meaning that you're hearing the aircraft now, and several seconds ago, all at once.
It's not an actual object, more a kind of fictional line of where the sound has reached. Any aircraft therefore produces one constant sonic boom, or infinite individual sonic booms, depending on your perspective
The 900 per minute is just internet silliness. As opposed to Internet seriousness, which is to be avoided at all costs.
Now in theory as you say, props passing the sound barrier could make lots of individual sound points, IE you hear the blades pass multiple times as they move towards and away from you vertically (around the propellor hub) - this would be significantly higher than 900 per minute, I'd have thought. So from that perspective you could hear the propellor create a staccato of boom-silence-boom.... But it wouldn't be as loud as the plane itself, and would only be heard as part of the plane passing. The propellor are still moving with the plane, remember.

The prop tips were supersonic even when the plane was idling on the ground so it's not just about the plane moving past the observer. Also, the internet seems to think that the noise of the supersonic prop itself was a significant contribution to the overall noise of the plane.

@DavidRicherby the same is true for many high performance helicopters around takeoff.

I'm not saying that it's a quiet aircraft, or that supersonic prop tips make no difference - just that the '900 sonic booms per minute' makes no real sense as a number to quite. Also prop booms are nowhere near the volume level of a passing supersonic aircraft - because the props are quieter in general, and because they're only heading toward the listener at supersonic speed for a fraction of a second (unlike an aircraft passing which is building up the pressure wave for a moment or two)

All aircraft have at least two sonic waves. While some people on the ground may perceive the sound as a single sonic “boom,” many sonic booms produced from NASA’s research flights are easily heard as distinct “double” booms, The Space Shuttle was notorious for its double boom. https://www.nasa.gov/centers/armstrong/news/FactSheets/FS-016-DFRC.html

A sonic boom is technically the same concept as thunder... It's air that moves over the aircraft and crashes together behind it resulting in the sound. I do highly doubt the XF-84H make 900 sonic booms a minute. I have done extensive research on it and one of the big misconceptions is they were trying to make a supersonic propeller driven aircraft when that's not the case. This goes a little off topic but in fact early jets were not that great and they wanted jet performance out of props, which is doable to an extent. Jets take time to accumulate their power where a prop is instantaneous with the use of variable pitch props. The engine on the Thunderscreech was in fact ran at full throttle all the time and the prop was adjusted to generate the needed power which was instant compared to a jet. I'm linking this article so I don't go too much into a huge chat about this, it's my favorite plane of all time... But read this, it's the most informative article I've read and it's got people from the project actually talking about things I've mentioned. https://www.airspacemag.com/how-things-work/zwrrwwwbrzr-4846149/

"It's air that moves over the aircraft and crashes together behind it resulting in the sound." is incorrect. "they were trying to make a supersonic propeller driven aircraft when that's not the case" whether they were trying or not is irrelevant: they ended up with an aircraft that ran its propeller tips at supersonic speeds.

"supersonic propeller aircraft" can be parsed two different ways.  I get the feeling that Kat meant it in the "supersonic ... aircraft" sense and Hobbes read it in the "supersonic propeller" sense.


text:
Can I land a plane in a field?
If I had a plane that could take off and land in a short distance (eg., the SD-1 Minisport), do I have to use a recognized airport in order to land in the US?  Or can I just land anywhere so long as it's class G airspace?
FYI, this question is for non-emergencies.  IE., if I just wanted to land there because it was convenient.

Just make sure you're not trespassing... :)

Landowner's permission is always required.  Then check the municipal zoning regulations and the like - city, state regs etc.  Then your insurance company.  If all these points come up green, go do it.

Note that (fixed-wing) insurance policies often forbid landing anywhere that is not designated as an airport (or seaplane base). You can still do it, but if something goes wrong the insurance company won't pay your claim. (You can get this restriction removed from most policies - it's just a matter of money...)

So, basically, there's no FAA regulations on it.  But there may be other objections?

No FAA prohibition that I know of.  But if you damage your plane or property on the ground, you may be looking at a "careless and reckless" charge from the FAA.  And yes there may well be other objections.

You can land wherever you want as far as the aviation regulations are concerned. The airspace is irrelevant. You may, however, be breaking a range of different state laws. Generally speaking, the things to watch out for:
(1) Landing on private property without express permission is trespassing
(2) Landing anywhere a person would be likely to be may be reckless endangerment
(3) Landing in such a way that would cause an unnecessary emergency response can result in a charge for intentional or careless use of emergency services (you can avoid this by calling them ahead of time and telling them you do not need emergency services)
In general, you can land on any public land that is not a place someone else would be (like a road). If you land on a road without good reason, it could be construed as reckless.
In remote areas like Alaska landing off field is routine and occurs as a matter of course.
Pilots that fly in back woods areas and land off field all the time are called "bush pilots".

If you know the landowner you can land on private land as well. There are tons of private airstrips listed on sectionals for advisory/emergency purposes. Any mapped facility has to meet minimum FAA regs (mainly surface quality, clearance from surrounding development, weather indicators etc) so these are regularly maintained and fairly permanent, but if your buddy living on 100 acres out in BFE doesn't mind clearing and mowing one of his flatter pastures to make a surface you'd want to try to land/take off from, you can fly out to his farm and use his field as you would any other airstrip.

I land in my backyard regularly.  It used to be that we could land on town roads years ago, but the laws changed.  Without a ground crew it wasn't really safe.
There are three farms within a mile of me who have 2000+ foot grass strips, and they get regular visitors.  My yard isn't groomed as much so thankfully few people drop in.
Some municipalities have created local ordinances against landing on site not approved by the town.  The legality of those ordinances is not clear.
My homeowner's insurance does not care, as I do not advertise and encourage the public.  My aircraft insurance does not have a restriction about uncharted or sod/dirt strips.
If you are new at the game, I suggest that you walk the field before hand, and already have experience landing on rougher grass or dirt.
The FAA is aware of my landing area, but I chose to not have it charted.  Just adds to map clutter, and anyone in the area with an emergency has a ton of alternatives, most of which are better.


text:
Why can planes generally take more positive g's than negative g's?
Most commercial airliners are rated to take +2.5g and -1.0g.  Why is this?  Is it designed that way on purpose?  To clarify, this would mean that the cost difference between -1g and -2.5 g is minuscule, so price (and thus engineering difficulty, which drives price) isn't really a factor.
Or, are there in fact significant difficulties with creating a frame that can handle a lot of negative Gs?  (And if there are, what are they?)

The gravity of Earth is +1g. So if the +2.5g and -1.0g ratings are correct, planes can take an extra positive 1.5g (2.5g-1.0g) but 2.0g lower than normal 1.0g-(-1.0g). Hope this makes any sense.

@collector It had occurred to me.  It almost makes it sound like they add a little structural reinforcement for negative G's since the difference from mean gravity is roughly neutral, with it being skewed towards negative Gs.  This works really well when the plane is right side up, but I've seen similar figures for fighter jets, which are designed to go upside down as well...  Anyway, you might spin that comment into an answer, maybe the community will agree with you :).

It's partly pragmatic (you start from +1.0 G, so why not optimize for that???) and partly because (most) aircraft are designed to carry human beings.  Humans as well as a lot of other things are FAR more tolerant of positive G-forces than they are negative G-forces.
There's very little technical reason that you couldn't design an aircraft wing and other structures to handle high negative G loads.  But adding that strength also means adding weight, complexity, and cost.  And since the benefit of being able to pull high negative G loads is pretty small, very few designers choose to do this.


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How is bleed air used to start a jet engine?
I know that most jet engines on commercial jets are started either with bleed air from an APU or bleed air from the other engine...  But I'm not exactly sure how bleed air actually starts the engine?
Is the bleed air just being blown into the compression chamber?  Or is it being used in some other way?

As a starting point, this question here has an answer that describes the entire process of starting a jet engine on a high level.  It includes a short section on bleed air:

Through the opening of bleed air valves, bleed air is sent to an air turbine starter. These devices typically use the high pressure bleed air to spin and engage a centrifugal clutch connected to the engines accessory drive. This in turn causes the N2 shaft within the engine to spin.

But I'm hoping for a more detailed explanation on what the bleed air is doing, how (and where) the clutch is applied (is there a transmission as well?).  Problems that may arise, and how they are dealt with.  Etc etc...  I just would like more detail if it's possible.

Related: Air Turbine Starters and Turbine starters and G-450

There are some youtube videos that show air start turbines in great detail. Would it be appropriate to post a link to one of them?


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How to achieve shorter taxiing time by elongating the airfield
What about doubling the length of airfields in order to shorten the time it takes for a plane to roll on the ground after landing and before takeoff. The plane could take off from the middle of the air-lane and when it lands it can turn off in the middle, in order to minimise the driving time to and from the terminal. Why don't we see this and what does it take to achieve it?
I had expected a calculation as an answer to this question. Taxiing takes 23 minutes. In Sweden savings for private travel is evaluated to €4 per hour and $20 for business.

Smaller planes can already do this at larger airports, it is known as an intersection takeoff.  And depending on where the destination is at the landing airport, we can turnoff the runway earlier once slowed down vs going all the way to the end of the runway.  It all depends on the size/speed of the aircraft; a large jet needs more rolling time both for takeoff & landing with all that momentum vs a small 2/4/6 seater that can be airborne and landed/slowed down in well under 2000 ft.

Or you could have two shorter runways side-by-side... Pretty sure that is very common throughout the world...

Cost is a good reason not to do this. Instead of having 2 9,000' parallel runways that are potentially useful simultaneously, you have 1 18,000' runway that you're only using half of.

Not quite to the same extent you have in mind, but when you are able to have a staggered set of runways, they will try to arrange it so that the "landing" ones have the roll out area near the terminal, and the "takeoff" ones have the threshold near the terminal.
Let's take BWI as an example.  In an south/east flow (takeoffs and landing heading south/east), all traffic will take off on 15R, right next to the NW end of the terminal.  All traffic will land on 10, with the exit from the rollout a little bit after the runways cross.
Or IAD, in a North flow, most landings will happen on 1R and takeoffs on 1C.
NAS (naval air station) Lemoore is another sort of example of this - kind of a little split because of the structure of the ramp, but if it was one terminal, in a NW flow  you'd have all takeoffs on the N runway and all landings on the S runway.
Put another way, if you have a 9000 foot runway, in your scheme you'd need to make 1 18000 foot runway, but it is at least twice as efficient to have 2x9000 ones, even if it increases the taxi time, and some of that can be mitigated by the staggering above.

Not so at KATL. Land on the outboards, depart on the inboards (with a midfield terminal).

@RetiredATC yes, it depends on geography and how the land is available.  NAS Lemoore as in my example is "optimized" for this sort of flow, but ATL can go both ways (and LAX,DFW)

The cost is that it would required a runway twice as long.
Airports already take up enormous amounts of land. Designers try to build airports near major centers, so taking up twice as much valuable land for longer runways near a major population center is a huge cost.
The longer runways also need to be cleaned, maintained, and snow-plowed.
That is a lot of cost and difficulty just to reduce taxi-time by a couple minutes.   After one has taken a 2 hour cross-country flight, 5 minutes of taxi-time is not a point of concern.

Denver International Airport was designed to minimize taxi times as well as allow for simultaneous parallel operations when necessary.  The runways are laid out in a 'pinwheel' with one end near the terminal. With a northerly wind you can land on 35L and 35R and roll out near the terminal on the east. Takeoffs can use 34L and 34R which start near the terminal on the west side. In bad weather you can use 34L and 35R to get the separation for parallel ops though the 34L aircraft will have a longer taxi.

Anyone who has landed at DIA may question that it minimizes taxi times.  I've often heard it joked that planes land at the Kansas Border, and drive in to Denver.

5 minutes taxiing for 200 passenger compares to a cost of say USD 1300, regardless of how long time the flight takes. Is there a calculation somewhere about savings and costs?

@abelenky  i said it was designed to - I didn't say it was successful. But it does apply a concept very similar to what the question proposes. And taxi times at DEN are typically better than DFW. Flying between DFW and AUS, it wasn't unusual to have taxi times at DFW greater than the flight time.

Cost? Concorde used 1200 kg of fuel just to taxi.

Notice that most airports are square-ish. For various reasons, it's usually a lot easier to get a compact parcel of land than a long, thin one.  In particular, aviation authorities really don't like roads going under runways, so the airport as a whole creates problems for the highway system around it; double the length of the runways and those problems get much worse.  In the old days, a square parcel was used to provide several (intersecting) runways at different angles, but many have been rebuilt to have parallel (and thus simultaneously usable) runways in the same compact area; taxi times might be a bit longer, but overall throughput is much, much higher.

As pointed out by Crossroads. Smaller aircraft use only a small portion of the runway. Therefore, they can and do start their takeoff rolls at other points accessible from taxiways other that the end of the runway. These are called intersection departures.
Most large aircraft and many smaller aircraft will avoid or decline intersection departures. Large aircraft must have the distance to be able to accelerate to takeoff speed, immediately decelerate from takeoff speed, and come to a complete stop before the end of the runway. Smaller aircraft benefit from maximizing the full length of the runway in order to have enough distance for landing on the same runway in case of an engine-out scenario while climbing out during departure.

In many cases, planes can already take off from the middle of a runway.  Elongating the runway is not the issue.  As an illustration, a runway that can accommodate a fully loaded 747 is at least 10000 feet.  Many hub runways are over 13000 feet.  The ATR-72 and E-175, both fairly common aircraft, need less than 5000 feet to take off.
You want to have aircraft park on the ramp in the middle of the runway and takeoff with minimal taxiing from the middle of the runway.  The reason this is impossible is that the ramp does not fit at the middle of the runway.
Take a look at these two recent airport designs (Daxing and Noida).

The terminal and ramp area is usually about 1/3 the length of the runway, and sometimes much more.  At smaller airports, the terminal and ramps are smaller, but the runway is too.  The ramp is still about 1/3 the length of the runway.
Since the ramp is so big, it makes more sense to add another runway at the other end of the ramp instead of making the existing runway longer.  This is exactly how Daxing and Denver airports are designed.

The Denver airport layout is not widely copied because most airports are built in places where land is more expensive.

Can you show a cost comparison between land and taxi time?


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How did the Concorde’s glide ratio vary from takeoff to supercruise?
I can't seem to get straight numbers on its glide ratio. One source claims 4:1 at takeoff and 12:1 at transonic speeds. But what about the supercruising phase that it's flight was optimized for?

It depends on the version:

A Model
B Model

Takeoff
3.94
4.24

Initial climb
4.97
5.58

Hold @250KTS & 10,000ft
9.27
13.1

Subsonic Cruise
11.47
12.92

Supersonic Cruise
7.14
7.69

Source: concordesst.com

Not even at the wayback machine.

Case Study by Aerospatiale and British Aerospace on the Concorde,
by Jean Rech and Clive S Leyman
ISBN (print): 978-1-56347-308-1eISBN: 978-1-60086-812-2
Publication Date: June 1, 1980.  Part of the AIAA Professional Study Series. Specifically, see figure 3.20 on page 3-21.

Also p11 of Nasa memo 75464, a translation of the original document (G. Cormery, 1977) which shows the difference between the two wings (planes A/B) and the efficiency gains.


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Is there a convention of propeller tip separation from the wind tunnel walls?
Blockage ratio is commonly used to address the effect of confinement on the propeller's performance tested inside a closed test section of a wind tunnel. In most cases, blockage corrections (like Glauert's) are applied to the measured velocity, assuming that the propeller was positioned along the centerline of the test section.

What happens if the propeller model is offset from the center? Would these corrections be equally valid in that scenario?

Is there a convention on how close the propeller tip could be to the wall before the wall starts to affect the slipstream significantly? Would experiments be the only option to check this out?

Thanks!

For your particular propeller and test cell, the most trustworthy check would be to try different offsets from center, both vertically and horizontally if the cell's cross section isn't square, and from that derive a secondary correction (since you know the prop didn't change).


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AN-225 dimensions?
Does anyone know the dimensions of the AN-225 tail or where I can find them? I am doing a research/personal development project, and my focus is on improving my CAD modelling skills. I am deeply interested in aviation and thought it would be cool to model the AN-225 tail for my project.
Thank you!

Not an answer, but some ideas: Knowing the main dimensions, it is easy to derive the other ones using a photo or a drawing. You can also use the photo or the drawing as a reference image in your CAD software, or download a 3D model and study it.

You can download magazine “Аэрохобби” 1/1992 (https://readli.net/aerohobbi-1992-01/). There are couple schemes that you may use and also description about sizes.


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What is this little "rod" thing on the back of the F-22 for?
I was curious what this little extra surface on the back of the F-22 is for. I can't see any use of it protruding past the engine nozzles, so what is it for? Also, does the structure have any problems with heating, being right beside the engines? (Especially with the afterburner on)

What is this jutting structure in the tail section called and what is its function?

That's how they make F-16's

Does this answer your question? What is this jutting structure in the tail section called and what is its function?

Always the flashy jets that have the tiny little wanker on them!

According to this cutaway (source) it is a "runaway emergency arrest hook housing":

It is the tailhook housing. Looking for a definitive picture, but can't find one.

but I thought the F-22 wasn't meant to be operated on carriers, or any situations needing a tailhook. Is it a backup then for emergencies?

@Wyatt - Yes, emergencies. Hooks aren't just for carriers. Most (All?) USAF fighters have a hook, F-15, -16, etc. And the runways have a cable at each end.

I believe that was something that started being used with the Air Force version of the F-4.

@Davidw - No, before then. The F-100 had an emer arresting hook as well.

While the cutaway drawing shows that Stinger described as an enclosure for the runaway arrestor hook, close-up inspection of an F-22 aft section reveals that is only partly true.

The runaway arrester hook is located in a low RCS blister pod just under that structure.
If you take a look at the aft end of an F119 engine removed from the airplane, you see quite a bit of structure surrounding the jet pipe. This contains the actuation equipment for the thrust vectoring paddles.

I would argue that the little ‘stinger’ is more likely an aerodynamic closeout or similar structure between the two engines once they are installed in the airplane.

I strongly support this answer, the tailhook has its own housing below the "stinger. I would add that the stinger (obviously) also has the function of controlling radar reflections. The center stinger is clearly split, this would suggest is may hold some active components. It is worth noting that publicly availlable information about F-22 is very limited for obvious reasons. The fact that the stinger is officially listed as tailhook housing absolutely does not mean it actually is only that.

Judging by the signature on the illustration, it appears to have been done in 1997.  That was the year the production F-22A was publicly rolled out and it’s unclear where the artist obtained the information for all of the details shown.  It’s possible he was employed by Lockheed and got it that way, but did not go into depth on this section of the a/c, or simply could not show it due to perspective, etc.

Btw, i think the two first images are 3D-models, not actual aircraft. Not that it would make too much difference since they are very high quality.


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Is it possible for a shockwave to reflect off of the ground, making the observer hear 2 shocks?
Is it possible for a shockwave from a supersonic aircraft to reflect off of the ground, forcing the observer to hear 2 shockwaves?

In this picture, the shockwave from this aircraft is shown to reach the ground. When oblique shockwaves contact an obstacle, they will reflect. Depends on the obstacle shape and type. (I don’t know for sure about those statements)
(I think that also depends on the medium the shock is coming into contact with, for example I don’t think a shock would reflect off of a very soft / fuzzy pillow or a sound absorbing material)
After it reflects, it would be heading back into the sky at an angle. Wouldn’t this make the observer hear 2 shocks? (The reflected one and original)

Seems more like a Physics question, rather than Aviation.

@RalphJ It has to do with aerodynamics, which is on topic for this site. But I do see where this wouldn’t really fit in, so if you would like to migrate it I wouldn’t mind.

Why should it be different then echo? So yes.

Rough terrain like that pictured would serve to scatter the reflected shock.  Lets imagine that the observer were on a hard smooth surface first.
Yes, they would hear two shocks -- however they would be so close together that the human ear probably couldn't really differentiate them.  When a supersonic aircraft flies over, the shock system has usually formed itself into an N-wave, which primarily consists of a shock at the front and another at the aft of the aircraft.  So, a sonic boom is often a double-boom already -- with the separation based on the speed of the aircraft and the length of the airplane (i.e. how long the airplane takes to fully pass).
You'll hear the reflection of the front shock well before the aft shock comes.  But again, the human ear may well muddle it all together.
Generally speaking, in acoustics, the ground reflection does tend to double the amplitude of a sound (+3dB).  Consequently, when we make certain kinds of measurements (meant to simulate free-air noise), we actually place the microphone on a hard plate at ground level.  That way, the mic only picks up the sound once.

"n-wave" is a new term for me. If it's new to anyone else, here's a definition from a US Air Force fact sheet.


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Does the pressure recovery become not as extreme as you speed up?
Does the pressure recovery area on a wing become not as intense as you speed up? If so, why?
The pressure recovery is the effect that decelerates the air after it has been accelerated by the airfoil. When you speed up, is this force reduced?

Here is a photo I found. (Ignore the arrows and the lines) So as you can see, the red area (low pressure) dissipates towards the rear of the airfoil. This is the pressure recovery area.
Does that pressure recovery effect decrease as you increase speed? If so, why does the pressure recovery area not recover as much pressure as you speed up?
(The low pressure also dissipates towards the tip of the wing, but that's not important to this question)
When air goes over the top of the airfoil, it will get accelerated, and therefore turn low pressure. In this picture, the red area is where this is happening. When the air is done accelerating and it is reaching the rear portion of the wing, it will start to decelerate due to the atmospheric pressure. The area of deceleration is the pressure recovery area.
This question is asking if this pressure recovery effect will decrease as you increase speed. (and if it does, why that is the case)
Here's my theory of why the pressure recovery becomes not as intense as you increase speed:

(In this case imagine the plate is an airfoil. It's hard to draw an airfoil, so I just used a plate as an example)
Imagine you have an airfoil facing into the wind. Like this one:
The blue arrows represent the airflow. So in this case, (if the flow is compressible) there would be high pressure on the front of it, and low pressure on the back. Not very surprising.
Now, put it at an angle.
In this case, there is still high pressure on the (now bottom) part of it, and there is still low pressure on the top. These effects are reduced, though. (because of the angle)
Remember that the adverse pressure gradient is the force that decelerates the flow after it has been accelerated by the wing. (it can also cause stalls to occur).
So in the picture above, the angle of the plate causes it to have low pressure above it (along with the effect of the airfoil shape causing low pressure, but I'm ignoring that). Because of this effect that makes the air above the plate low pressure, wouldn't the adverse pressure gradient or pressure recovery also become lower pressure? Meaning that the adverse pressure wouldn't be as strong?

"the back pressure decreases as you increase speed" do you mean Bernoulli?

maybe what he's asking about is just as the aircraft begins to move...  This aspect is discussed in detail by Jones.

Sorry everyone, this seems like it's a hard to understand question. Maybe @sophit this answer / question will help explain what I'm asking. Basically, where the pressure recovery is, that force, why does it change as you speed up. Bernoulli will change the pressure on the wing, but what changes the back pressure on the wing. The back pressure is the force decelerating the air at the rear of the airfoil. Will edit the question to make it more clear.

Hey, Wyatt - some of us are low speed people (literally), and need a moment to get our heads around this.  We don't think so much about compressibility issues and Mach effects, but consider flight issues below Mach 0.3+/- where this is not a problem.

@sophit Did that edit help somewhat? If not I can try to improve it some more.

@ThomasPerry Oh okay haha. I understand that. Maybe that edit I just did helped out?

"When the air is done accelerating and it is reaching the rear portion of the wing, it will start to decelerate due to the atmospheric pressure" not really.due to the atmospheric pressure, it starts decelerating AND the pressure raising just because this is the effect of airfoil upon the air flowing around it.

The example with the vertical airfoil is not helpful because it is dominated by separated flow whereas the effect you mention first is happening in the linear range of aerodynamics where flow is attached. Also, high pressure in the front is the consequence of stagnating flow, not compressibility.

I find it very hard to understand your questions because you choose strange wording for things which have proper names already.
Why should there be a change in the pressure distribution as speed increases? We can use dimensionless parameters (coefficients) to describe a pressure distribution because speed has no influence on it. It does have an influence on the absolute pressure change (that grows with the square of speed), but not the distribution. This is especially true at low Mach numbers; once you cross into transsonic flow, the Mach number increase from the speed increase will have an effect on the pressure distribution.
What you probably mean is the change due to a lower angle of attack as the airplane flies faster but still needs the same lift to fly. With the increase in speed the angle of attack has to be reduced to keep the forces in equilibrium.
From potential flow theory we know that the pressure distribution over an airfoil is the linear combination of lift due to angle of attack plus lift due to camber. A lower angle of attack reduces its share of the total so that the resulting pressure distribution more and more resembles the pure camber distribution as angle of attack is reduced.
Since pressure variations grow with the square of speed, I cannot agree that any pressure should "reduce as speed goes up". Suction will get stronger, as will dynamic pressure, but neither will be reduced.
So far, I have left density out of the picture. Include it, and it will be better to use dynamic pressure as a proxy for speed. You can always trade an increase in speed for a decrease in density; that is why airliners want to fly high up in the troposphere.
Dynamic pressure can be seen as equivalent to the stiffness of a spring. Increase it, and forces will increase and oscillations will speed up. That is why higher dynamic pressure will also cause higher absolute pressure variations. There is only one standard speed at which pressure changes, and that is the speed of sound. In fully subsonic flow, pressures will adjust practically immediately to changes in the flow field.

"It does have an influence on the absolute pressure change (that grows with the square of speed), but not the distribution." Interesting. So say you're traveling at mach 0.2. The air accelerates over the top of the wing and turns low pressure. If you go faster (say mach 0.4), the air will be even lower pressure. The air (mach 0.4) will have less time to 're pressurize' when it is going faster over the foil (re pressurize after it's been accelerated), so wouldn't that mean the air traveling off of the rear of the airfoil would still be low pressure? Both mach 0.2 and 0.4 cases at the same AoA.

Something I needed to include : The reason it will take longer for the air to ' re pressurize' is because it is lower pressure. It takes more time to fill a section of air that is a vacuum than it does to fill a section of air that's just a few psi below atmospheric, for example.

(If that doesn’t make sense I will make an edit to my question)

@Wyatt See, now I understand much better where you are stuck. Please see the added paragraph, it should not really surprise you after all what you have read here already. And yes, please edit your question, so others will be less confused than I was yesterday.

@Wyatt and please change the awful "back pressure" phrase to something better suited. You used "pressure recovery" yourself, so please stick to the accepted phrases.

I see, that edit helped a lot! I will be editing this question, and also changing the back pressure phrase. Thanks.

I edited the question, let me know if there's anything else I could improve!

@Wyatt Oh boy, where do I start ... pressure recovery is an effect, not a force. And why should it shrink when speed increases? Please name your source or ask an open question. When you start with an incorrect assumption you will not arrive at a better understanding when you do not question that assumption. ALL forces grow more intense when you speed up, so please stop thinking that some force will decrease when speed increases (and all other parameters stay constant).

Ah okay. I make another edit changing "force" to "effect". I also attempted to explain why I thought the pressure recovery effect would shrink as speed increased. I'm not too confident that it will make sense, but I will keep trying.

@Wyatt Please do not simply change single words and append new stuff at the end. Instead, rework the whole text so it becomes consistent. And don't say "it is well known", followed by a falsehood. Better ask an open question ("Is it true that ... if yes, why?")

I removed the part about the pressure distribution of the wing changing, because that isn't really what this question is about. (although I did ask you follow up questions about that) I also removed the statements, and turned them into questions. Is that better? It seems to still be getting downvoted, so maybe not. After following your advice I think the question looks a lot better, so not sure why.

@Wyatt What you call a photo is actually a drawing I made with Inkscape for this answer.

Yes that’s exactly where I got the drawing. (Looks very professional!) I can edit the question again to add the source.

@Wyatt No, no, i don't need attribution, but please do not call it a photo!

Oh okay, I also think drawing is more appropriate.

It may be, in a relative sense, that delta P is less because the Volume of air passing over the wing (to produce the same amount of lift) will be greater.
For the same lift at higher speed, angle of attack will be less, and the amount of deflection of the airstream is less.
Keep in mind the downwash created by the bottom of the wing also lowers pressure behind the wing and may contribute to the acceleration of air over the top of the wing.
If the wing moves more rapidly away from a given parcel of air, one might also imagine, relative to the wing, pressure is lower.
An analogy might be the Doppler effect with sound.  The whistle of a passing train drops in pitch as it passes, just as a person on the train would notice the same effect if a stationary person sounded a horn.